The present disclosure relates to the subject matter contained in Japanese Patent Application No.2002-76724 filed on Mar. 19, 2002, which are incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to an image forming apparatus based on electrophotography, such as a copying machine, printer, facsimile machine, and a complex machine having the functions of those machines. More particularly, the invention relates to the improvement of the arrangement of a plurality of fixing devices and the control of it.
2. Description of the Related Art
A known electrophotography-basis image forming apparatus, for example, such a color image forming apparatus as a color copying machine or a color printer, has the following construction. The image forming apparatus is provided with only one photo receptor drum. Color toner images of yellow (Y), magenta (M), cyan (C), black (BK), and the like are successively formed on the photo receptor drum. The color toner images of yellow (Y), magenta (M), cyan (C), black (BK), and the like, which are successively formed on the photo receptor drum, are transferred onto a recording sheet in a superimposing fashion. Those toner images are heated and fused onto the recording sheet, to thereby form a color image. In another known color image forming apparatus, the color toner images of yellow (Y), magenta (M), cyan (C), black (BK), and the like, which are successively formed on the photo receptor drum, are primarily transferred onto the intermediate transfer body in a superimposing fashion. Those color, toner images having been transferred onto the intermediate transfer body are secondarily transferred onto a recording sheet simultaneously. Those toner images are heated and fused on the recording sheet to thereby form a color image.
Yet another known color image forming apparatus is provided with a plurality of image forming units of yellow (Y), magenta (M), cyan (C), black (BK), and the like. The color toner images of yellow (Y), magenta (M), cyan (C), black (BK), and the like, which are successively formed onto the photo receptor drums of the image forming units, are transferred onto a recording sheet in a superimposing fashion or primarily transferred onto the intermediate transfer body. The color toner images having been transferred onto the intermediate transfer body are secondarily transferred onto the recording sheet simultaneously. Those toner images are heated and fused on the recording sheet to thereby form a color image.
The color toner that is transferred and fused onto the recording sheet, normally, is formed such that a colorant made of pigment or dyestuffs is dispersed or molten and mixed into binder resin. The particle diameter is selected to be several xcexcm to several tens xcexcm. Such color toners are transferred onto a plain paper or coated paper, e.g., general printing paper, in a state that a plurality of layers of color toner are superimposed, and then fixed onto a plain paper or coated paper, e.g., general printing paper, while being heated and molten. At this time, an undulation of the toner layer makes the surface of the color image uneven of 10 to 100 xcexcm in height, and hence, its surface gloss is made irregular. As a result, the color image formed on a plain paper or coated paper, e.g., general printing paper, reflect diffusely incident illumination light When observed by the naked eye, the color image is poor in glossiness.
The following techniques for producing images with good glossiness are known.
JP-A-5-127413 discloses a color image forming method in which a transparent resin layer is located on the surface of a transfer body, and color toner is fixed on the transparent resin layer to thereby form a color image. The resultant image is rich in tone, excellent in color reproducibility, high in resolution, and good in glossiness. The color image forming method disclosed by JP-A-5-127413 melts and fixes the color toner onto the transfer body to form a color image. In the image forming method, the transparent resin layer formed of at least thermoplastic resin, 20 to 200 xcexcm thick, is located on the surface of the transfer body. Color toner of 3 to 9 xcexcm in volume averaged grain size is stuck onto the transparent resin layer by the quantity of 0.2 to 4.0 mg/cm2, and then heated, molten and fixed to form a color image.
JP-B-4-31389 and JP-B-4-31393 disclose techniques of a picture quality improving method and a picture quality improvement processing device. In those publications, a sheet is applied on a fixed toner image which has been discharged from the image forming apparatus, and heated under pressure. Then, the sheet is cooled and stripped off the toner image. A shape of the sheet surface is replicated to provide a glossy image.
A possible approach to produce a color image forming apparatus capable of forming a color image having good glossiness is that a toner image, not yet fixed, is formed on the recording sheet by image forming unit, such as a known color copying machine or a color printer, is fixed by fixing means, and second fixing unit, additionally provided, further fixes the image on the recording sheet to thereby increase the glossiness of the toner image.
The following power consumption problem arises in the image forming apparatus having first and second fixing unit, however.
Usually, the commercial AC source power is frequently used up to its tolerable upper limit power, 1.5 kVA (100 V, 15 A), in order to secure higher copying productivity for plain papers.
When examining the items of its power consumption, the power consumption by the fixing unit for fusing and fixing the toner image by thermal energy is large, generally 600 to 1000 W. The power consumption of the image processing and image forming sections other than the fixing means is approximately 800 W.
The second fixing unit for the gloss increasing process further consumes electric power of 700 to 1,300 W by its heating source. Additionally, electric power of 250 W is consumed by the image processor for high quality image, and power of 50W, for the driving of the second fixing unit and its cooling fan driving. When the first and second fixing unit are concurrently driven, the maximum power consumed by the whole apparatus, greatly exceeds 1.5 kVA, and reaches a value near 3.0 kVA.
Even if two electrical outlets of the commercial power source are provided, the power consumption by the image forming apparatus must be 2.0 kVA at the maximum in use environments of general offices and homes since the 20 A breaker is used for the main power source. To use the electric power of 2.0 kVA or higher, extensive power supply work is required in use environments, and this should be avoided if possible.
Accordingly, an object of the present invention is to provide an image forming apparatus, which is capable of producing an image of high gloss without increasing the power capacity.
According to a first aspect of the invention, there is provided an image forming apparatus having an image forming unit for forming an unfixed toner image on a recording sheet, a first fixing unit for fixing the unfixed toner image on the recording sheet, a second fixing unit for further fixing the toner image on the recording sheet, which is fixed by the first fixing unit, and a control unit for selecting one of a first fixing mode in which only the first fixing unit is used for fixing the toner image on the recording sheet and a second fixing mode in which the first and second fixing unit are used for the fixing. Width of the recording sheet, which the second fixing unit can fix is narrower than that of the recording sheet, which the first fixing unit can fix. For example, the width of the recording sheet (for example, the long side of A4), which the second fixing unit can fix is narrower than the half (for example, the post card width and the width of the photograph of L size) of the width of the recording sheet, which the first fixing unit can fix.
According to a second aspect of the invention, there is provided an image forming apparatus having an image forming unit for forming an unfixed toner image on a recording sheet, a first fixing unit for fixing the unfixed toner image on the recording sheet at a predetermined temperature, a second fixing unit for further fixing the toner image on the recording sheet, which is fixed by the first fixing unit, and a control unit for selecting one of a first fixing mode in which only the first fixing unit is used for fixing the toner image on the recording sheet and a second fixing mode in which the first and second fixing unit are used for the fixing. The control unit sets the predetermined temperature of the first fixing unit in the second fixing mode to be lower than that of the first fixing unit in the first fixing mode.
According to a third aspect of the invention, there is provided an image forming apparatus having an image forming unit for forming an unfixed toner image on a recording sheet, a first fixing unit including a first heating source, the first fixing unit for fixing the unfixed toner image on the recording sheet, a second fixing unit including a second heating source, the second fixing unit for further fixing the toner image on the recording sheet, which is fixed by the first fixing unit, and a control unit for controlling electric power supplied to the first and second heating sources. The control unit executes such a control that a timing of supplying electric power to the first heating source is not coincident with a timing of supplying electric power to the second heating source.
According to a fourth aspect of the invention, there is provided an image forming apparatus having an image forming unit for forming an unfixed toner image on a recording sheet, a first fixing unit including a first heating source, the first fixing unit for fixing the unfixed toner image on the recording sheet at a first predetermined temperature, a second fixing unit including a second heating source, the second fixing unit for further fixing the toner image on the recording sheet, which is fixed by the first fixing unit at a second predetermined temperature, and a control unit for controlling electric power supplied to the first and second heating sources. When temperature of the first fixing unit and temperature of the second fixing unit are below the first and second predetermined temperature, respectively, the control unit supplies electric power to one of the first and second heat source, which is smaller in thermal capacity than the other. A thermal capacity of the first fixing unit may be smaller than that of the second fixing unit.
According to a fifth aspect of the invention, there is provided an image forming apparatus having an image forming unit for forming an unfixed toner image on a recording sheet, a first fixing unit including a first heating source, the first fixing unit for fixing the unfixed toner image on the recording sheet, a second fixing unit including a second heating source, the second fixing unit for further fixing the toner image on the recording sheet, which is fixed by the first fixing unit, and a control unit for controlling electric power supplied to the first and second heating sources. The second heating source includes a plurality of heating source elements; and wherein the control unit supplies electric power to the second heating source so that a quantity of heat generated by the second heating source at a timing of supplying electric power to the first heating source is smaller than that at a timing of supplying no electric power to the first heating source.
When the second heating source includes a plurality of heating source elements, electric power may be supplied to the heating source elements of the second heating source so that a quantity of heat generated by the second heating source at the timing of supplying electric power to the first heating source is smaller than that at the timing of supplying no electric power to the first heating source. In the image forming apparatus, the second heating source includes two heating source elements which are different in generated heat quantity, and at the timing of supplying electric power to the first heating source, the control unit supplies electric power to one of the two heating source elements forming the second heating source, which is smaller in generated heat quantity, and at the timing of supplying no electric power to the first heating source, the control unit supplies electric power to one of the two heating source elements forming the second heating source, which is larger in generated heat quantity.
The invention provides an image forming apparatus having an image forming unit for forming an unfixed toner image on a recording sheet, a first fixing unit including a first heating source, for fixing the unfixed toner image on the recording sheet, a second fixing unit including a second heating source, for further fixing the toner image on the recording sheet, which is fixed by the first fixing unit, and a control unit for controlling electric power supplied to the first and second heating sources. The second heating source includes three heating source elements. The control unit performs such a control that the timings of supplying electric power to the first heating source and one of the heating source elements of the second heating sources are not coincident with each other, and that the timings of supplying electric power to the remaining two heating source elements of the second heating source are not coincident with each other. The maximum power consumption by the first heating source is preferably equal to the maximum power consumption by one of the heating source elements of the second heating sources. Preferably, the maximum power consumption by the remaining two heating source elements are (substantially) equal to each other. The maximum power consumption by one of the heating source elements of the second heating source is larger than that by the remaining two heating source elements.
According to a sixth aspect of the invention, there is provided an image forming apparatus having an image forming unit for forming an unfixed toner image on a recording sheet, a first fixing unit including a first heating source, the first fixing unit for fixing the unfixed toner image on the recording sheet, a second fixing unit including a second heating source, the second fixing unit for further fixing the toner image on the recording sheet, which is fixed by the fist fixing unit, and a control unit for controlling electric power supplied to the first and second heating sources. When electric power is simultaneously supplied to the first heating source and the second heating source, the control unit supplies cut-off power to the first and second heating sources so that the sum of supplied electric power is below a predetermined power value.
1) In the image forming apparatus, the preset power value may be below a maximum power consumption value which is the larger of the maximum power consumption values of the first heating source and second heating source.
2) The preset power value may be equal to a maximum power consumption value which is the larger of the maximum power consumption values of the first heating source and second heating source.
3) The maximum power consumption values of the first heating source and second heating source are preferably equal to each other.
The technical ideas of the first to sixth image forming apparatus may appropriately combined to another image forming apparatus. To this end, the technical ideas of the first and second image forming apparatus maybe combined. The technical ideas of the third and fourth image forming apparatus may also be combined. Further, the technical ideas of the first image forming apparatus and/or second image forming apparatus and the third image forming apparatus and/or fourth image forming apparatus may be combined for the same purpose. The technical ideas of the first image forming apparatus and/or the second and fifth image forming apparatus may be combined. Additionally, the first image forming apparatus and/or second image forming apparatus and the sixth image forming apparatus may also be combined, if necessary.
The second fixing unit may include a plurality of rolls, and an endless belt stretched around the rolls, and a recording sheet is brought into close contact with a surface of the endless belt, and cooled, and peeled off the endless belt.